1. Field of the Invention
The present invention relates to a display device having a display screen whose aspect ratio is 16:9 and a display device having a display screen whose aspect ratio is 4:3 and, particularly, to a display device in which a displaying method is improved such that it can display an image whose aspect ratio is different from these aspect ratios of the display screen.
2. Description of the Related Art
Recently, a video screen having an aspect ratio of 16:9 which provides better presence than that obtainable by a conventional aspect ratio of 4:3 is developed for such as high-difinition TV reception, etc., and is becoming popular. With such recent tendency, a display device having display screen whose aspect ratio is 16:9 has become commercially available to display a video image having its aspect ratio of 16:9 or a conventional video image having its aspect ratio of 4:3. Further, a display of video image having its aspect ratio of 16:9 has been also attempted to be displayed on a conventional display device having a display screen having its aspect ratio of 4:3. That is, it has been tried to display, on a display screen of a display device, a video image whose aspect ratio is different from that of the display screen.
When a video image whose aspect ratio is 4:3 is displayed on a display screen of 16:9 aspect ratio, any of the following three methods are conceivable:
(1) An image of 4:3 aspect ratio is displayed on a center of a display screen having the aspect ratio of 16:9 by adjusting with a vertical length (height) of the image being matched with a vertical length of the screen, as shown in FIG. 1(A) so that the original aspect ratio of the image is maintained leaving unfilled areas at both sides of the screen. This is realized by deflecting the electron beam horizontally within a hatched range in FIG. 1(A) or time-compressing the video signal. PA1 (2) An image of 4:3 aspect ratio is displayed on a display screen having the aspect ratio of 16:9 by adjusting a horizontal length (width) of the image being matched with a horizontal length of the screen while an upper and lower edge portions of the image being cut off, as shown in FIG. 1(B). This is realized by deflecting electron beam vertically over a hatched range in FIG. 1(B). PA1 (3) An image of 4:3 aspect ratio is displayed on a display screen having the aspect ratio of 16:9 by adjusting a vertical length of the image so as to match the height of the screen and expanding linearly a horizontal length of the image to fill the screen as shown in FIG. 1(C). In this case, the original aspect ratio of the image is no longer maintained. PA1 (4) An image of 16:9 aspect ratio is displayed on a center portion of a display screen having the aspect ratio of 4:3 by adjusting a horizontal length of the image being matched with a horizontal length of the screen, as shown in FIG. 2(A) so that the aspect ratio of the image is maintained. This is realized by deflecting the electron beam vertically within a hatched range in FIG. 2(A). PA1 (5) An image of 16:9 aspect ratio is displayed on a display screen having the aspect ratio of 4:3 by adjusting a vertical length of the image being matched with a vertical length of the screen while a right and left portions of the image being cut off, as shown in FIG. 2(B). This is realized by deflecting the electron beam horizontally over a hatched range in FIG. 2(B) or time-expanding the video signal. PA1 (6) An image of 16:9 aspect ratio is displayed on a display screen having the aspect ratio of 4:3 by adjusting a horizontal and a vertical length of the image being matched with horizontal and vertical lengths of the screen by linearly compressing the image horizontally and linearly expanding the image vertically to fill the screen as shown in FIG. 2(C). PA1 In the method (1) or (4) in which an image is displayed on a part of a screen, the size of the displayed image is inevitably small. Further, since straight boundaries between the displayed image and an unfilled screen area (a pair of black belts) are visible, a raster distortion (if any) looks conspicuous. In addition, when this display mode is used for a long period of time, a permanent difference in raster luminance between the used portion and the unused portion of the screen of a cathode ray tube, may develop as a "burnt screen". PA1 In the method (2) or (5), it is impossible to watch the cut-out portions of the image. PA1 the first circuitry for non-linearly expanding a horizontal display scale of the 4:3 image being fully displayed to fill up the 16:9 screen, in right and left portions of the image relative to the horizontal center of the image as such that a rate of non-linear expansion is increased as a horizontal position within the image becomes distant from a horizontal center of the image; and PA1 the second circuitry for non-linearly compressing a vertical display scale of the 4:3 image being fully displayed to fill up the 16:9 screen, in upper and lower portions of the image relative to the vertical center of the image as such that a rate of non-linear compression is increased as a vertical position within the image becomes distant from a vertical center of the image. In the latter device, the horizontal scale is non-linearly compressed, and the vertical scale is non-linearly expanded. PA1 the first circuitry for non-linearly compressing a horizontal display scale of the 16:9 image being fully displayed to fill up the 4:3 screen, in right and left portions of the image relative to the horizontal center of the image as such that a rate of non-linear compression is increased as a horizontal position within the image becomes distant from a horizontal center of the image; and PA1 the second circuitry for non-linearly expanding a vertical display scale of the 16:9 image being fully displayed to fill up the 4:3 screen, in upper and lower portions of the image relative to the vertical center of the image as such that a rate of non-linear expansion is increased as a vertical position within the image becomes distant from a vertical center of the image. PA1 the second circuitry for non-linearly compressing a horizontal display scale of the visible picture being fully displayed to fill up the 4:3 display screen, in right and left portions of the visible picture with respect to a horizontal center portion of the visible picture in such a manner that a rate of non-linear compression is increased as a horizontal position within the visible picture becomes distant from a horizontal center of the visible picture; and PA1 the third circuitry for non-linearly expanding a vertical display scale of the visible picture being fully displayed to fill up the 4:3 display screen, in upper and lower portions of the visible picture with respect to a vertical center portion of the visible picture in such a manner that a rate of non-linear expansion is increased as a vertical position within the visible picture becomes distant from a vertical center of the visible picture.
On the other hand, when a video image of 16:9 aspect ratio is displayed on a display screen of a display device, whose aspect ratio is 4:3, any of the following three methods is conceivable:
Further, there is a video image of so-called vista size, which is transmitted as a 4:3 aspect ratio image signal, but its visible area has an aspect ratio of 16:9, such image may be displayed as it is within a screen of 4:3 aspect ratio as shown in FIG. 2(A), or such image may be displayed in such manner as shown in any of FIGS. 2(B) and 2(C).
However, these conceivable methods (1) to (6) have the following drawbacks:
In the method (3), an image displayed is distorted since the original 4:3 image is no longer maintained, instead, the original image is vertically compressed and horizontally expanded.
This is also true for the method (6) in which the original 16:9 aspect ratio image is no longer maintained, instead, the original image is vertically expanded and horizontally compressed.